NEFL and Cognitive impairment: In detail, blood NfL was associated with cognitive impairment in a heterogeneous PD cohort with 596 participants applying DRS-2 score (Aamodt et al. 2021), in 301 de novo PD patients from the Parkinson’s Progression Markers Initiative (PPMI) using MoCA (Ma et al. 2021), and in 178 participants with moderate disease stages from a Taiwanese study assessed with MMSE (Lin et al. 2019) as well as in 289 advanced PD patients examined with MoCA (Choe et al. 2020; Niemann et al. 2021).